Particle beam accelerator, particle beam blocking method for particle beam accelerator, and particle beam therapy apparatus

ABSTRACT

According to one embodiment, a particle beam accelerator comprising: a guiding unit configured to guide a particle beam to a trajectory; an acceleration unit configured to accelerate the particle beam circulating on the trajectory; a particle beam blocking unit configured to block the particle beam on the trajectory; and a control unit configured to control the guiding unit, the acceleration unit, and the particle beam blocking unit, wherein: the guiding unit includes a superconducting electromagnet and a superconducting electromagnet interrupter configured to interrupt the superconducting electromagnet, and the control unit is configured to interrupt the superconducting electromagnet by activating the superconducting electromagnet interrupter after completion of blocking the particle beam by activating the particle beam blocking unit, when an abnormality occurs in the superconducting electromagnet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of No. PCT/JP2021/038452, filed on Oct. 18, 2021, and the PCT application is based upon and claims the benefit of priority from Japanese Patent Application No.2020-203781, filed on Dec. 8, 2020, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

Embodiments of the present invention relate to a technique for particle beam acceleration

BACKGROUND

In recent years, attention has been focused on a particle beam therapy technique in which a patient's diseased tissue such as cancer is irradiated with a particle beam of carbon ions for treatment. Since this particle beam therapy technique can pinpoint and kill only the diseased tissue without damaging normal tissues, the burden on the patient is less than surgery or medication treatment, and earlier return to society after the treatment can also be expected.

In order to treat cancer cells deep inside the body, it is necessary to accelerate the particle beam. In general, particle beam accelerators configured to accelerate the particle beam are broadly classified into two types. One of the two types is a linear accelerator in which a high-frequency acceleration cavity is arranged in a straight line, and the other type is a circular accelerator in which a deflectors configured to bend the trajectory of a particle beam are arranged approximately circularly and a high-frequency acceleration cavity is disposed in part of this circular trajectory. In particular, for heavy particles such as carbons and protons, it is common to adopt the method in which a linear accelerator is used for acceleration in the low energy band immediately after generation of the particle beam and a circular accelerator is used for acceleration in the high energy band.

The circular accelerator configured to circulate and accelerate the particle beam is configured by sequentially arranging: a focusing/defocusing apparatus configured to control the shape of the particle beam; a deflector configured to bend the trajectory of the particle beam; and a steering electromagnet configured to correct deviation of the trajectory of the particle beam. In this circular accelerator, when mass or energy of the circulating particles increases, magnetic rigidity (i.e., difficulty of bending due to the magnetic field) increases and thus the trajectory radius of the particle beam increases. As a result, the entirety of the apparatus including the circular accelerator becomes large in size. As the size of the apparatus increases, the incidental facilities in the building also increase in size, which makes it difficult to introduce this apparatus in a place where the installation range is limited, such as in an urban site.

In order to suppress increase in size of the circular accelerator, it is necessary to increase the magnetic field strength to be generated by the deflector. Ina general deflector, though influence of magnetic saturation of its iron core makes it difficult to generate a magnetic field exceeding 1.5 T, application of superconducting technology to the deflector enables enhancement in magnetic field strength and thus enables reduction in size of the circular accelerator. However, if an abnormality such as quenching occurs in the superconducting electromagnet constituting the deflector of the circular accelerator for the particle beam therapy apparatus, there is a possibility that the particle beam is erroneously radiated to the patient.

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] JP 2019-141245 A

[Patent Document 2] JP 2015-159060 A

[Patent Document 3] JP 2017-033978 A

SUMMARY Problems to be Solved by Invention

An object of the present invention is to reduce a risk of erroneous irradiation of a particle beam by properly maintaining the particle beam in a predetermined trajectory in a particle beam accelerator.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a charged particle beam therapy apparatus.

FIG. 2 is a plan view illustrating a superconducting synchrotron.

FIG. 3 is an electric circuit diagram illustrating a superconducting electromagnet apparatus.

FIG. 4 is a block diagram illustrating a control system in the superconducting synchrotron.

FIG. 5 is a timing chart illustrating change in current value of a superconducting electromagnet and change in particle beam intensity in the case of simultaneously activating both a superconducting electromagnet interrupter and a charged particle beam blocker.

FIG. 6 is a timing chart illustrating change in current value of the superconducting electromagnet and change in particle beam intensity when the superconducting electromagnet interrupter is activated after completion of blocking the charged particle beam by the charged particle beam blocker.

DETAILED DESCRIPTION

In one embodiment of the present invention, a particle beam accelerator comprising: a guiding unit configured to guide a particle beam to a trajectory; an acceleration unit configured to accelerate the particle beam circulating on the trajectory; a particle beam blocking unit configured to block the particle beam on the trajectory; and a control unit configured to control the guiding unit, the acceleration unit, and the particle beam blocking unit, wherein: the guiding unit includes a superconducting electromagnet and a superconducting electromagnet interrupter configured to interrupt the superconducting electromagnet, and the control unit is configured to interrupt the superconducting electromagnet by activating the superconducting electromagnet interrupter after completion of blocking the particle beam by activating the particle beam blocking unit, when an abnormality occurs in the superconducting electromagnet.

Hereinbelow, embodiments of a particle beam accelerator, a particle beam blocking method for a particle beam accelerator, and a particle beam therapy apparatus will be described in detail by referring to the accompanying drawings.

As shown in FIG. 1 , a charged particle beam therapy apparatus 10 as a particle beam therapy apparatus according to the present embodiment is an apparatus that uses charged particles (for example, negative pions, protons, helium ions, carbon ions, neon ions, silicon ions, and argon ions) as a charged particle beam source for therapeutic irradiation. This charged particle beam therapy apparatus 10 includes: a particle beam generator 11; a particle beam accelerator 12; a particle beam transport apparatus 13; and a particle beam irradiator 14. This charged particle beam therapy apparatus 10 irradiates a lesion site 5 of a patient as an irradiation target with a charged particle beam 1. The charged particle beam 1 is used to treat the lesion site 5.

The particle beam generator 11 is an apparatus that generates the charged particle beam 1 and is, for example, an apparatus that extracts ions and the like generated by using an electromagnetic field or a laser.

The particle beam accelerator 12 is an apparatus that accelerates the charged particle beam 1 to a predetermined energy. As one aspect, FIG. 1 illustrates a configuration provided with two-stage accelerators that is composed of a front-stage accelerator 15 and a rear-stage accelerator 16. Aspects of the front-stage accelerator 15 include a linear accelerator such as a drift tube linac (DTL) and a radio-frequency quadrupole linear accelerator (RFQ). Aspects of the rear-stage accelerator 16 include a circular accelerator such as a synchrotron and a cyclotron.

The particle beam accelerator 12 includes: a vacuum. duct 20 (piping) configured to keep the passage space of charged particle beam 1 vacuum and airtight; a high-frequency acceleration cavity 24 configured to accelerate the charged particle beam 1 by an electric field; deflectors 21 configured as dipole electromagnets to stably guide the charged particle beam 1; and focusing/defocusing apparatuses 22 configured as quadrupole electromagnets; and a controller 30 configured to control each of these components.

The particle beam transport apparatus 13 is a system that transports the charged particle beam 1 accelerated by the particle beam accelerator 12 to the particle beam irradiator 14. The particle beam transport apparatus 13 includes: a vacuum duct; deflectors; focusing/defocusing apparatuses; and a controller configured to control these components.

The particle beam irradiator 14 is installed at the downstream of the particle beam transport apparatus 13. In order to accurately irradiate the irradiation point having been set at the lesion site 5 of the patient with the charged particle beam 1 that has passed through this particle beam transport apparatus 13 and has specific energy, the particle beam irradiator 14 adjusts the trajectory 3 of the charged particle beam 1 and further monitors the irradiation position and irradiation dose of the charged particle beam 1 at the lesion site 5.

FIG. 2 shows a superconducting synchrotron 17 as the rear-stage accelerator 16 of the particle beam accelerator 12 described above. This superconducting synchrotron 17 is an apparatus that accelerates the charged particle beam 1 while circulating the charged particle beam 1. The superconducting synchrotron 17 is configured by arranging: a plurality of deflectors 21; a plurality of focusing/defocusing apparatuses 22; a plurality of hexapole electromagnets 23; a high-frequency acceleration cavity 24; a beam injector 25; abeam emitter 26; and a charged particle beam blocker 27, on the outer diameter side of the ring-shaped vacuum duct 20. The superconducting synchrotron 17 further includes a controller 30.

The vacuum duct 20 is piping that keeps the passage space of the charged particle beam 1 vacuum and airtight. On its axis, a predetermined trajectory 3 through which the charged particle beam 1 passes is formed.

Each deflector 21 is composed of a dipole electromagnet, and circulates the charged particle beam 1 along the predetermined trajectory 3 by the magnetic field to be generated. Each focusing/defocusing apparatus 22 is composed of a quadrupole electromagnet, and focuses or defocuses the charged particle beam 1 circulating on the predetermined trajectory 3 by the magnetic field to be generated. Thus, the deflectors 21 and the focusing/defocusing apparatuses 22 function as a guiding unit that stably guides the charged particle beam 1 along the predetermined trajectory 3.

The high-frequency acceleration cavity 24 functions as an acceleration unit configured to accelerate the charged particle beam 1 circulating along the predetermined trajectory 3 in the vacuum duct 20 by an electric field that is generated by applying a high-frequency voltage. In addition, the beam injector 25 functions as an injection unit configured to inject the charged particle beam 1 generated by the particle beam generator 11 into the superconducting synchrotron 17. Further, the beam emitter 26 functions as an emission unit configured to emit the charged particle beam 1 accelerated by the superconducting synchrotron 17 to the particle beam transport apparatus 13.

The charged particle beam blocker 27 functions as a particle beam blocking unit configured to urgently block the charged particle beam 1 circulating on the predetermined trajectory 3 inside the vacuum duct 20. This blocking by the charged particle beam blocker 27 is, specifically, blocking of the charged particle beam 1 by closing a gate (not shown), blocking of the charged particle beam 1 by a bump electromagnet (not shown) configured to deviate the charged particle beam 1 into a disposal orbit, or the like. In addition, the controller 30 functions as a control unit configured to control the deflectors 21, the focusing/defocusing apparatuses 22, the hexapole electromagnets 23, the high-frequency acceleration cavity 24, the beam injector 25, the beam emitter 26, and the charged particle beam blocker 27 described above.

Each of the above-described deflectors 21 and the focusing/defocusing apparatuses 22 includes a normal-conducting electromagnet in general. In the present embodiment, either or both of each deflector 21 and each focusing/defocusing apparatus 22 is configured as a superconducting electromagnet apparatus 31 that includes a superconducting electromagnet 32 shown in FIG. 3 . This superconducting electromagnet apparatus 31 is configured by: connecting the superconducting electromagnet 32, an excitation power supply 33, and a circuit breaker 34 in series; and connecting a protective resistance 35 to the superconducting electromagnet 32 in parallel.

When an abnormality such as quenching occurs in the superconducting electromagnet 32, a quench detector (not shown) outputs a quench signal and thereby the circuit breaker 34 opens. This opening operation of the circuit breaker 34 forms a closed circuit in which the superconducting electromagnet 32 and the protective resistance 35 are connected in series. As a result, the energy stored in the superconducting electromagnet 32 is consumed by the protective resistance 35 and the superconducting electromagnet 32 is disconnected. Thus, the above-described circuit breaker 34 and the protective resistance 35 constitute the superconducting electromagnet interrupter 28 configured to interrupt the superconducting electromagnet 32.

In either or both the focusing/defocusing apparatuses 22 and the deflectors 21 configured as the superconducting electromagnet apparatuses 31, an abnormality such as quenching may occur in the superconducting electromagnet 32. When the charged particle beam blocker 27 (FIG. 2 ) and the superconducting electromagnet interrupter 28 (FIG. 3 ) are activated at the same time, it causes a problem. For example, as shown in FIG. 5 , it is assumed that both: blocking of the charged particle beam 1 by the charged particle beam blocker 27; and interruption of the superconducting electromagnet 32 by the superconducting electromagnet interrupter 28 are simultaneously started. When the current value of the superconducting electromagnet 32 subjected to quenching or the like changes (decreases) before completion of blocking the charged particle beam 1, there is a possibility that the charged particle beam 1 before completion of blocking deviates from the predetermined trajectory 3.

When the charged particle beam 1 deviates largely from the predetermined trajectory 3, the charged particle beam 1 collides with the vacuum duct 20 and is lost. When the charged particle beam 1 deviates slightly from the predetermined trajectory 3, there is a possibility that the charged particle beam 1 reaches the position of the patient so as to be erroneously radiated to an unexpected site of the patient by the particle beam irradiator 14, for example, a site outside the lesion tissue.

For this reason, when the controller 30 of the present embodiment receives a quench signal in response to occurrence of an abnormality such as quenching in the superconducting electromagnet 32 of the superconducting electromagnet apparatus 31 constituting either or both the deflector 21 and the focusing/defocusing apparatus 22, the controller 30 first activates the charged particle beam blocker 27 so as to block the charged particle beam 1 as shown in FIG. 4 and FIG. 6 . After completion of blocking the charged particle beam 1, the superconducting electromagnet interrupter 28 is activated to interrupt the superconducting electromagnet 32 in which quenching or the like has occurred.

As a result, as shown in FIG. 6 , the current value of the superconducting electromagnet 32 subjected to quenching or the like does not decrease and is maintained at an appropriate value during the period from the start of blocking the charged particle beam 1 to its completion, and thus, the charged particle beam 1 is blocked without deviating from the predetermined trajectory 3 in the superconducting synchrotron 17.

As shown in FIG. 3 , a resistance value of the protective resistance 35 of the superconducting electromagnet apparatus 31 is set in such a manner that an interruption time constant Ta of the superconducting electromagnet interrupter 28 is longer than a blocking time constant Tb of the charged particle beam blocker 27. The interruption time constant Ta is the time length from the start of interrupting the superconducting electromagnet 32 to its completion. The blocking time constant Tb is the time length from the start of blocking the charged particle beam 1 to its completion.

In other words, the interruption time constant Ta of the superconducting electromagnet interrupter 28 is determined by selecting the resistance value of the protective resistance 35 depending on rise in coil temperature and generated voltage at the time of occurrence of quenching (or the like) in the superconducting electromagnet 32, and is set to approximately ten seconds or less, for example.

Since the blocking of the charged particle beam 1 by charged particle beam blocker 27 is achieved by closing of the gate or deviation of the beam by the bump electromagnet, the blocking time constant Tb of the charged particle beam blocker 27 is set to approximately 100 milliseconds or less. Thus, the interruption time constant Ta of the superconducting electromagnet interrupter 28 is longer than the blocking time constant Tb of the charged particle beam blocker 27, i.e., the blocking time constant Tb of the charged particle beam blocker 27 is set sufficiently shorter than the interruption time constant Ta of the superconducting electromagnet interrupter 28. Hence, generation of large voltage and rise in coil temperature in the superconducting electromagnet 32 subjected to quenching or the like is suppressed as much as possible.

The present embodiment has the above-described configuration and thus has the following effects.

As shown in FIG. 2 to FIG. 4 , when an abnormality (for example, quenching) occurs in the superconducting electromagnet 32 of either or both the deflector 21 and the focusing/defocusing apparatus 22 in the superconducting synchrotron 17 as the particle beam accelerator 12, first, the charged particle beam blocker 27 is activated. After completion of blocking the charged particle beam 1, the superconducting electromagnet interrupter 28 is activated to interrupt the superconducting electromagnet 32 in which quenching or the like has occurred. Hence, as shown in FIG. 6 , the blocking of the charged particle beam 1 can be completed in the state where the current value of the superconducting electromagnet 32 subjected to the quenching or the like does not decrease and is at an appropriate value. As a result, in the superconducting synchrotron 17, the charged particle beam 1 before the completion of blocking does not deviate from the predetermined trajectory 3, and thus, it can reduce the risk of erroneous irradiation of the charged particle beam 1 emitted from superconducting synchrotron 17 by the particle beam irradiator 14.

As shown in FIG. 3 , the resistance value of the protective resistance 35 of the superconducting electromagnet apparatus 31 is set in such a manner that the interruption time constant Ta of the superconducting electromagnet interrupter 28 is longer than the blocking time constant Tb of the charged particle beam blocker 27. Thus, the blocking time constant Tb of the charged particle beam blocker 27 becomes sufficiently shorter than the interruption time constant Ta of the superconducting electromagnet interrupter 28. Hence, when an abnormality such as quenching occurs in the superconducting electromagnet 32 of the superconducting electromagnet apparatus 31, even in the case of waiting for blocking of the superconducting electromagnet 32 subjected to the quenching (or the like) for time length of the blocking time constant Tb of the charged particle beam blocker 27, rise in coil temperature and generation of large voltage in the superconducting electromagnet 32 subjected to the quenching (or the like) can be suppressed due to the sufficiently short blocking time constant Tb. As a result, occurrence of burnout in the superconducting electromagnet 32 subjected to the quenching or the like can be avoided.

The controller 30 of the present embodiment includes hardware resources such as a Central Processing Unit (CPU), a Read Only Memory (ROM), a Random Access Memory (RAM) and/or a Hard Disk Drive (HDD), and is configured as a computer in which information processing by software is achieved with the use of the hardware resources by causing the CPU to execute various programs. Further, the particle beam blocking method for the particle beam accelerator of the present embodiment is achieved by causing the computer to execute the various programs.

The controller 30 in the present embodiment includes a storage device such as the ROM and the RAM, an external storage device such as the HDD and a Solid State Drive (SSD), a display device such as a display panel, an input device such as a mouse and a keyboard, a communication interface, and a control device which has a highly integrated processor such as a Field Programmable Gate Array (FPGA), a Graphics Processing Unit (GPU), the CPU, and a special-purpose chip. The controller 30 can be achieved by hardware configuration with the use of the normal computer.

Note that each program executed in the controller 30 of the present embodiment is provided by being incorporated in a memory such as the ROM in advance. Additionally or alternatively, each program may be provided by being stored as a file of installable or executable format in a non-transitory computer-readable storage medium such as a CD-ROM, a CD-R, a memory card, a DVD, and a flexible disk (FD).

In addition, each program executed in the controller 30 may be stored on a computer connected to a network such as the Internet and be provided by being downloaded via a network. Further, the controller 30 can also be configured by interconnecting and combining separate modules, which independently exhibit respective functions of the components, via a network or a dedicated line.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

1. A particle beam accelerator comprising: a guiding unit configured to guide a particle beam to a trajectory; an acceleration unit configured to accelerate the particle beam circulating on the trajectory; a particle beam blocking unit configured to block the particle beam on the trajectory; and a control unit configured to control the guiding unit, the acceleration unit, and the particle beam blocking unit, wherein: the guiding unit includes a superconducting electromagnet and a superconducting electromagnet interrupter configured to interrupt the superconducting electromagnet, and the control unit is configured to interrupt the superconducting electromagnet by activating the superconducting electromagnet interrupter after completion of blocking the particle beam by activating the particle beam blocking unit, when an abnormality occurs in the superconducting electromagnet.
 2. The particle beam accelerator according to claim 1, wherein: the superconducting electromagnet interrupter includes a circuit breaker and a protective resistance and interrupts the superconducting electromagnet by opening the circuit breaker to form a closed circuit between the superconducting electromagnet and the protective resistance; and a resistance value of the protective resistance is set in such a manner that an interruption time constant of the superconducting electromagnet interrupter is longer than a blocking time constant of the particle beam blocking unit.
 3. A particle beam blocking method for a particle beam accelerator that comprises: a guiding unit configured to guide a particle beam to a trajectory; an acceleration unit configured to accelerate the particle beam circulating on the trajectory; and a particle beam blocking unit configured to block the particle beam on the trajectory, wherein: the guiding unit includes a superconducting electromagnet and a superconducting electromagnet interrupter configured to interrupt the superconducting electromagnet, and the superconducting electromagnet is interrupted by activating the superconducting electromagnet interrupter after completion of blocking the particle beam by activating the particle beam blocking unit, when an abnormality occurs in the superconducting electromagnet.
 4. A particle beam therapy apparatus comprising: the particle beam accelerator according to claim 1; and a particle beam irradiator configured to irradiate a lesion site of a patient with the particle beam accelerated by the particle beam accelerator for treatment. 